Hydraulic load compensating directional control valve



Sept. 16, 1969 BALLARD ETAL 3,467,126

HYDRAULIC LOAD COMPENSATING DIRECTIONAL CONTROL VALVE Filed March 21, 1966 J 2 Sheets-Sheet 1 I HYDRAULIC ACTUATOR l... 1

ACTUATOR I so (;2 i as I I 44 FIG 2 I BY ATTORNEYS United States Patent US. Cl. 137-115 4 Claims ABSTRACT OF THE DISCLOSURE A hydraulic control valve system is provided to control the operation of a hydraulic actuator in a load compensating manner such that any given control setting will operate the hydraulic actuator at the same velocity regardless of the load conditions on the hydraulic actuator. The load compensating valve also provides overload relief protection for the hydraulic fluid supply pump.

This invention relates to hydraulic fluid control systems providing velocity and directional control of hydraulic actuator mechanisms. More particularly, this invention relates to hydraulic valve systems for controlling hydraulic actuators.

Hydraulic actuators, for example hydraulic motor and hydraulic cylinders, are often required to operate against varying loads and at varying speeds or velocities, a typical example being an hydraulically-operated fork lift wherein hydraulic cylinders must raise or lower the fork lift when various sized loads are placed thereon and must raise or lower the fork lift at various speeds or velocities. As the load increases, the pressure of the hydraulic fluid supplied to the hydraulic actuator must be increased cornmensurately so that the hydraulic actuator can handle the increased load. When the hydraulic actuator is to be operated at a greater speed, the flow of the hydraulic fluid supplied to the hydraulic actuator also must be increased commensurately.

Known control systems for hydraulic actuators cannot compensate for load changes or velocity changes in a manner such that a predetermined control setting will provide a predetermined hydraulic actuator velocity regardless of the load. For example, the control setting in known control systems for slowly raising a non-loaded hydraulically-operated fork lift from a stationary position probably would not be suflicient to even slightly budge the fork lift loaded to five hundred or one thousand pounds, and certainly would not be suflicient to raise the loaded fork lift at the same speed as when unloaded. Consequently, operating personnel must acquire considerable skill in adjusting the control settings of known control systems to operate hydraulic actuators under various loads and velocity conditions.

A primary object of this invention is to provide an hydraulic control valve system for controlling an hydraulic actuator that is load compensating such that any given control setting will operate the hydraulic actuator at the same velocity regardless of the load conditions on the hydraulic actuator. Another object is to provide such a control system for directionally controlling an hydraulic actuator. A further object is to provide such a control system wherein the hydraulic actuator velocity is linearly adjustable by a linear control setting adjustment. Still another object is to provide such a control system affording improved overload relief protection for an hydraulic fluid supply pump. A still further object is to provide such a control system enabling an hydraulic fluid supply pump to be unloaded when the control system is placed in a neutral position.

These and other objects and advantages of this invention will become apparent from the following disclosure in conjunction with the accompanying drawings, of which:

FIG. 1 is a graphical diagram of a basic control valve system of this invention employing a tandem center fourway directional control valve;

FIG. 2 is a cutaway diagram of a control valve system similar to the FIG. 1 graphical diagram but with a closed center four-way directional control valve;

FIG. 3 is a graphical diagram of another embodiment of a control valve system of this invention employing a partially-blocked center four-way directional control valve with counter balance valves; and

FIG. 4 is a graphical diagram of still another embodiment of a control valve system of this invention employing a closed center four-way directional control valve with cross line relief valves.

In brief, the hydraulic control valve system of this invention comprises a directional control valve means and a load compensating valve means. The directional control valve means controls hydraulic fluid supply to an hydraulic actuator means. The load compensating valve means maintains a substantially constant hydraulic fluid pressure drop through the directional control valve means regardless of hydraulic actuator load changes and velocity changes. The load compensating valve means maintains the aforesaid constant pressure drop by regulating hydraulic fluid flow from the hydraulic fluid supply means to the directional control valve means and by returning excess hydraulic fluid to the hydraulic fluid supply means. With reference to the figures, the directional control valve means and the compensating valve means are designated in their entireties by the numerals 10 and 12, respectively.

The directional control valve means comprising a housing 13 provided with an inlet or pressure port 14 adapted to be connected to a pump 16 of an hydraulic fluid supply means 17 by a working line 18, a pair of outlet or cylinder ports 20 and 22 adapted to be connected to either side of an hydraulic actuator 24 by working lines 26 and 28, and one or more reservoir return or tank ports 30 adapted to be connected to a reservoir 32 of the hydraulic fluid supply means 17 by one or more working lines 34. A directional valving element 36 is provided in the housing to adjustably open and close off the ports 14, 20, 22 and 30 such that hydraulic fluid can be supplied from the hydraulic fluid supply means to the hydraulic actuator through either of the Working lines 26 or 28, and such that the directional control valve means can be placed in neutral to stop the flow of hydraulic fluid to the hydraulic actuator, the latter position being shown in the figures.

The valving element 36 shown in FIG. 2 is of the sliding spool type which is fitted to a bore through the longitudinal axis of a valve body and has lands which divide the bore into a series of separate chambers so that the position of the spool determines which ports are open to each other and which are sealed off from each other. Spool positioning may be accomplished manually, mechanically, electrically, hydraulically, or by combinations thereof. A spool type element is preferred because linear flow characteristics are more easily attainable by proper design of a sliding spool. Valving elements such as a rotary spool or other elements which provide a range of fluid flow may be employed, however. Valving element 36 may be adjusted by any desired actuating means such as by lever 38 pivotally connected to the housing 13 by linkages 40. Port land 42 is contoured to provide metering grooves or metering tapers (the later being shown in FIG. 2 at 41) for metering control between the pressure port 14 and the cylinder ports 20 and 22. The grooves or tapers provide a substantially linear relationship between hydraulic fluid flow and displacement of the valving element 36 when there is a substantially constant pressure drop across the pressure port, i.e. from the pressure port to the cylinder ports. These grooves or tapers are so formed that there is essentially no deadband so that any shift of the valving element from neutral (dead-center) will result in hydraulic fluid flow. A predetermined hydraulic fluid flow will pass through the directional control valve means 10, regardless of the load pressure at the cylindrical ports 20 and 22, so long as the pressure differential between the pressure and cylinder ports remains substantially constant.

The load compensating valve means 12 comprises a housing 44 provided with an inlet port 46 connected to working line 18 by a working line 48, an outlet port 50 adapted to be connected to reservoir 32 by a working line 52, and a pilot inlet port 54. The pilot port 54 communicates with working lines 26 and 28 by pilot lines 56 and 58 which are connected in parallel to the respective working lines 26-28 and by pilot line 60, the latter being connected to pilot port 54. The pilot lines 56 and 58 are provided with load sensing check valves 62 and 64, respectively, which allow a load pressure sample to be introduced to the pilot port 54, regardless of which working line 26-28 is subject to load pressure, and without pressure blending between the pilot lines 56-58.

A sliding spool-type valving element 66 is provided in the housing 44 with end lands 66a and 66b. Through internal pilot line porting in the housing, hydraulic fluid supply pressure from inlet port 46 is exerted on the outer end of land 66b and load pressure from pilot port 54 is exerted on the outer end of land 66a. Land 66a is sufficiently wide to close the outlet port 50. The valving element 66 is spring loaded by spring 68 at the pilot port end and the valving element 66 is therefore urged away from the pilot port to an outlet port sealing position as shown in FIG. 2. The intermediate stem portion 66c of the valving element is formed so that hydraulic fluid from working line 18 can pass through the inlet and outlet ports 46 and 50 when the hydraulic fluid supply pressure exceeds the load pressure plus the spring rate of spring 68 and thereby shifts the valving element to expose the outlet port 50. Thus, the hydraulic fluid supply pressure in Working line 18 will exceed the load pressure in either working line 26 or working line 28 by a substantially constant value essentially equal to the spring rate of spring 68.

If the load pressure increases, the valving element 66 will be shifted to restrict or close the outlet port 50 thereby substantially instantaneously forcing the hydraulic fluid supply pressure to increase to re-esta'blish the constant pressure drop across valve means 10. This point is reached when the resistance to flow through valve means and 12 is equalized such that any further supply pressure increase will cause the hydraulic fluid supply to bypass valve means 10 and return to the reservoir through valve means 12. If the load pressure decreases, the valving element 66 will be shifted to open the outlet port 50 thereby drawing hydraulic fluid supply away from pressure port 14 until the supply pressure at pressure port 14 falls to a point where the constant pressure drop across valve means 10 is reestablished. If the valving element 36 is shifted to increase the hydraulic fluid supply flow through valve means 10, the supply pressure at the pressure port 14 will decrease thereby decreasing the pressure drop across valve means 10. This pressure drop increase will result in valving element 66 closing off outlet port 50 so that the supply pressure at pressure port 14 will be raised to re-esta'blish the constant pressure drop across the valve means 10. If the valving element 36 is shifted to decrease the hydraulic fluid supply flow through valve means 10 the supply pressure at the pressure port 14 will increase, thereby increasing the pressure drop across valve means 10. This pressure increase will result in valving element 66 opening outlet port 50 to pass excess hydraulic fluid .4 supply to the reservoir until the supply pressure at pressure port 14 is lowered to re-establish the constant pressure drop across valve means 10. The four above-mentioned operating changes, namely increase or decrease in load pressure and increase or decrease in hydraulic fluid supply flow, will effect an essentially instantaneous reaction by valve means 12 thereby substantially instantaneously reestablishing the constant pressure drop across valve means 10. The regulation of hydraulic fluid supply to the pressure port of valve means 10 as described above in combination with the linearity of the pressure port land 42 provides the result that any given control setting of the actuating means for the directional control valve means will effect the same velocity for the hydraulic actuator regardless of the load on the hydraulic actuator. Furthermore, since the compensating valve means ibleeds off excess hydraulic fluid at some pressure greater than load pressure by a predetermined amount, e.g. 200 p.s.i., a reduction in pump power consumption and heat generation can be effected.

If it is desired to unload the hydraulic fluid supply pump when a partially-closed center directional control valve means is in neutral a small unobstructed reverse-flow orifice may be provided in each load sensing check valve, as at 70 and 72. Thus, when the directional control valve means is in neutral, load pressure is relieved from the pilot port end of the valving element 66 through the orifices 70-72 and cylinder ports 20-22 to tank thereby effecting a shift in valving element 66 that opens outlet port 50. The pump then can unload through the load compensating valve means to a pressure essentially equal to the spring rate of spring 68.

The load compensating valve means can provide overload relief protection for the hydraulic fluid supply pump. Overload relief protection is provided by an adjustable spring biased piston type relief valve assembly 74 communicating with the pilot 54 and with the outlet port 50 by internal porting in the housing 44. When load pressure exceeds the spring setting of the relief valve assembly, the piston lifts off its seat to allow fluid to pass from the pilot port 54, across the piston to the outlet port 50 and to the reservoir. An orifice 76 is provided in pilot line 60 so that when load pressure lifts the piston off its seat to allow fluid to pass from the pilot port to the outlet port 50, a pressure drop will occur across the orifice 76..

When this orifice pressure drop exceeds the spring rate of spring 68, the valving element 66 will shift to open outlet port 50 so that excess hydraulic fluid supply is passed to the reservoir to unload the pump until the supply pressure returns to the desired level.

The directional valving element for the directional control valve means can be provided with any flow path characteristic in center position as determined by circuit requirements. FIGS. 3 and 4, for example, depict directional control valve means having center position flow paths that are different from that depicted in FIG. 1 as required by their circuit requirements externally of the directional control valve means. FIG. 3 depicts a partiallyclosed center flow path characteristic and FIG. 4 depicts a closed center characteristic as required by the addition of counter balance valves 78 and 80 to the working lines 26 and 28 of the FIG. 3 system and by the addition of cross line relief valves 82 and 84 to the working lines 26 and 28 of the FIG. 4 system, respectively.

We claim:

1. An hydraulic valve system which comprises directional control valve means for controlling hydraulic fluid flow from hydraulic fluid supply means to hydraulic actuator means, said directional control valve means having a pressure port and at least one cylinder port and control means for regulating hydraulic fluid flow from said pressure port to said cylinder port; and compensating valve means having a fluid inlet port communicating with said pressure port, a fluid outlet port communicable with said hydraulic fluid supply means, and a pilot port communicating with said cylinder port, and a valving element normally closing said outlet port and responsive to pressure changes at said fluid inlet port and at said pilot port to open said fluid outlet port to passage of hydraulic fluid from said fluid inlet port responsive to changes in hydraulic fluid pressure difierential between said pressure port and said cylinder port such that hydraulic fluid flow to said pressure port is regulated to maintain such pressure differential substantially constant at a predetermined value; and a spring biased release valve assembly communicating with said pilot port and with said fluid outlet port to vent hydraulic fluid from said pilot port to said fluid outlet port when the pressure at said pilot port exceeds a predetermined value, and means providing an orifice between said cylinder port and said pilot port to eflect a pressure drop at said pilot port suflicient to cause said valving element to open said fluid outlet port when hydraulic fluid vents from said pilot port to said fluid outlet port.

2. An hydraulic valve system according to claim 1 wherein said; valving element comprises a spring-biased sliding spool type member provided in a bore such that pressure at said pilot port acts on said spool-type member to exert a force in combination with a spring bias force and such that pressure at said fluid port inlet acts on said spool-type member to exert a counter force.

3. An hydraulic valve system according to claim 1 wherein said control means for regulating hydraulic fluid flow from said pressure port to said cylinder port comprises a spool valving element with a contoured pressure port land providing a substantially linear relationship between hydraulic fiuid flow and displacement of said spool valving element when said pressure differential is maintained substantially constant.

-4. An hydraulic valve system which comprises directional control valve means for controlling hydraulic fluid flow from hydraulic fluid supply means to hydraulic actuator means, said directional control valve means having a pressure port and two cylinder ports and, a sliding spool type valving element with a pressure port land controlling hydraulic fluid flow from said pressure port to a selected one of said two cylinder ports, said pressure port land being contoured to provide a substantially linear relationship between hydraulic fluid flow and displacement of said sliding spool valving element for a substantially constant pressure differential between said pressure port and said. one cylinder port; compensating valve means having an inlet port communicating with said pres sure port, an outlet port communicable with said hydraulic fluid supply means, a pilot port communicating with each of said cylinder ports, and a spring biased sliding spool valving element with an outlet port land controlling hydraulic fluid flow through said outlet port, said spring biased sliding spool valving element normally closing said outlet port and being responsive to pressure changes at said inlet port and at said pilot port to open said outlet port when the pressure differential between said pressure port and a selected cylinder port increases above a predetermined value; a spring biased release valve assembly communicating with said pilot port and with said outlet port to vent hydraulic fluid from said pilot port to said outlet port when the pressure at said pilot port exceeds a predetermined value, and means providing an orifice between said selected cylinder port and said pilot port to effect a pressure drop at said pilot port sutficientto cause said spring biased spool valving element to open said outlet port when hydraulic fluid vents from said pilot port to said outlet port; and load sensing check valves communicating with said pilot port and said cylinder port.

References Cited UNITED STATES PATENTS 2,214,817 9/1940 Harrington l3 7l08 X 3,128,789 4/1964 Wagner 137---117 X 3,145,734 8/1964 Lee et al. 137-117 X 3,234,957 2/1966 Allen 137596.12 X

WILLIAM F. ODEA, Primary Examiner DAVID J. ZOBKIW, Assistant Examiner US. Cl. X.R. 137-596. l 2 

